1. Field of the Invention
The present invention relates to a zoom lens system and an image pickup system having the zoom lens system, and in particular relates to a zoom lens system in which picked-up images are stabilized by optically correcting image deflection produced when the zoom lens system is vibrated (inclined). The zoom lens system according to the present invention is suitable for an imaging optical system, such as a silver-film camera, a video camera, and a digital still camera.
2. Description of the Related Art
If vibration is incidentally transmitted to an imaging system, image deflection is produced in picked-up images. Various zoom lenses having a mechanism to compensate for the image deflection due to the incidental vibration (image stabilizer) have been proposed. For example, an optical system is known in which part of a lens unit constituting an optical system (zoom lens) is moved in a direction substantially perpendicular to an optical axis so as to compensate for the image deflection due to vibration.
A zoom lens disclosed in Japanese Patent Laid-Open No. 2-35406 (corresponding to U.S. Pat. No. 5,270,857) is mainly suitable for a taking lens of lens shutter cameras. The reference discloses a configuration in which part of a 3-unit zoom lens composed of a first lens unit with negative refractive power, a second lens unit with positive refractive power, and a third lens unit with negative refractive power, which are arranged in that order from an object to the image side, is moved in a direction substantially perpendicular to an optical axis so as to compensate for image deflection.
A zoom lens disclosed in Japanese Patent Laid-Open No. 5-224160 is mainly suitable for a telephoto zoom lens of single lens reflex cameras. The reference discloses a configuration in which a 5-unit zoom lens is composed of a first lens unit with positive refractive power, a second lens unit with negative refractive power, a third lens unit with positive refractive power, a fourth lens unit with positive refractive power, and a fifth lens unit with positive refractive power, which are arranged in that order from an object to the image side. The units with negative refractive power are moved in a direction substantially perpendicular to an optical axis so as to compensate for image deflection.
A zoom lens disclosed in Japanese Patent Laid-Open No. 8-136862 (corresponding to U.S. Pat. No. 6,124,972) is mainly suitable for a standard zoom lens of single lens reflex cameras. The reference discloses a configuration in which a 4-unit zoom lens is composed of a first lens unit with positive refractive power, a second lens unit with negative refractive power, a third lens unit with positive refractive power, and a fourth lens unit with positive refractive power, which are arranged in that order from an object to the image side. The second lens unit is moved in a direction substantially perpendicular to an optical axis so as to compensate for image deflection.
A zoom lens disclosed in Japanese Patent Laid-Open No. 10-282413 (corresponding to U.S. Pat. No. 6,061,180) is mainly suitable for a standard zoom lens of single lens reflex cameras. The reference discloses a configuration in which a 6-unit zoom lens is composed of a first lens unit with positive refractive power, a second lens unit with positive refractive power, a third lens unit with negative refractive power, a fourth lens unit with positive refractive power, a fifth lens unit with negative refractive power, and a sixth lens unit with positive refractive power, which are arranged in that order from an object to the image side. The fifth lens unit is moved in a direction substantially perpendicular to an optical axis so as to compensate for image deflection.
A zoom lens disclosed in Japanese Patent Laid-Open No. 2002-162564 (corresponding to US Patent Application Publication No. 2002101661) is mainly suitable for a large-aperture telephoto zoom lens of single lens reflex cameras. The reference discloses a configuration in which a 5-unit zoom lens is composed of a first lens unit with positive refractive power, a second lens unit with positive refractive power, a third lens unit with negative refractive power, a fourth lens unit with positive refractive power, and a fifth lens unit with positive refractive power fixed during zooming, which are arranged in that order from an object to the image side. The fifth lens unit, composed of a lens subunit with negative refractive power and a lens subunit with positive refractive power, is moved in a direction substantially perpendicular to an optical axis so as to compensate for image deflection.
Japanese Patent Laid-Open No. 10-90601 (corresponding to U.S. Pat. No. 6,025,962) discloses a configuration in which a 5-unit zoom lens is composed of a first lens unit with positive refractive power, a second lens unit with negative refractive power, a third lens unit with positive refractive power, a fourth lens unit with negative refractive power, and a fifth lens unit with positive refractive power fixed during zooming, which are arranged in that order from an object to the image side. The fourth lens unit is moved in a direction substantially perpendicular to an optical axis so as to compensate for image deflection.
In general, a mechanism for obtaining still images by vibrating a lens unit of an imaging system so as to eliminate image deflection requires that a degree of correction of the image deflection be large, the displacement and the rotational displacement of a lens unit (image stabilizer lens unit) to be vibrated for correcting the image deflection be small, and the entire apparatus be small in size.
As is well known, if a large amount of decentration aberration is produced when the image stabilizing lens unit is decentered, images become obscure when the image deflection is corrected. Hence, in an optical system having an image stabilizing function, it is required that the amount of decentration aberration produced when the image stabilizing lens unit is decentered be small (Problem 1), and large image deflection can be corrected with a small displacement of the image stabilizing lens unit, i.e., the vibration-proof sensitivity (the ratio ΔX/ΔH of the correction amount of image deflection ΔH to the unit displacement of the image stabilizing lens unit ΔX) be large (Problem 2).
However, in a zoom lens with a high zoom ratio in which the focal distance at the telephoto end is large, solving Problems 1 and 2 has been difficult at the zooming position of the telephoto end.
When the zoom lens disclosed in Japanese Patent Laid-Open No. 2-35406 is applied to an interchangeable lens of single lens reflex cameras, the back focal distance may be insufficient for securing the driving space of a QR mirror (quick return mirror).
The zoom lens disclosed in Japanese Patent Laid-Open No. 8-136862 is a standard zoom lens mainly used for single lens reflex cameras; however, the entire configuration is composed of a 4-unit lens zoom lens, so that it is difficult to increase the zoom ratio.
The zoom lenses disclosed in Japanese Patent Laid-Open No. 10-90601, Japanese Patent Laid-Open No. 10-282413, and Japanese Patent Laid-Open No. 2002-162564 are respectively composed of a front lens group having variable power and a rear lens group with positive refractive power, so that the lens unit with negative refractive power in the subsequent units is moved, as an image stabilizing lens unit, in a direction substantially perpendicular to an optical axis so as to compensate for image deflection. This configuration is advantageous for miniaturizing the image stabilizing lens unit and securing the large vibration-proof sensitivity. The zoom lenses disclosed in Japanese Patent Laid-Open No. 5-224160 and Japanese Patent Laid-Open No. 2002-162564 are telephoto lenses and since the focal distance at the telephoto end is large, it has been difficult to apply these optical systems to a standard zoom lens.
Also Japanese Patent Laid-Open No. 10-282413 discloses a standard zoom lens including a wide angle range; however, it has been difficult to apply it to a zoom lens with a further larger focal length at the telephoto end. The zoom lens disclosed in Japanese Patent Laid-Open No. 2002-162564 has a small back focal distance, so that when it is applied to an interchangeable lens of single lens reflex cameras, the interference with the quick return mirror may be produced.